Yeah, I was thinking of lobsters. I knew they were related, but I wasn't sure how closely related so I wasn't sure if they were actually the same species or phylum.
Well I was going to start an internet fight with you about this, but seeing as I have the whole internet here in my house, I just looked it up. Their phylum is both arthropod (not suprisingly), but once you get to the family level, things start to differentiate, even within lobsters themselves.